1. Field of the Invention
The present invention relates to lenticular media and, more particularly, to a method and apparatus for fabricating lenticular sheets optimally matched to a particular printer""s performance characteristics, and for controlling a printer to conform to particularities of and the orientation of the fabricated lenticular sheet.
2. Statement of the Problem
The use of lenticular sheets to transmit images to appear to an observer as three-dimensional, and to appear different from different viewer positions, to give a perception of changing as the observer moves, is known. A summary of certain typical features, and some general examples, are given for convenience.
A lenticular sheet, as it is generally known, includes a plurality of semi-cylindrical lenses, or lenticules, arranged side-by-side, in a plane, each extending in the same direction. The lenticular sheet is typically formed of a substantially transparent plastic and is overlaid onto an ink-supporting substrate or medium on which a plurality of specially formatted images are disposed.
If the lenticular sheet is to transmit images to appear three dimensional, the plurality of images disposed on the underlying medium includes one or more left images and, typically, a corresponding number of right images. Each left image and right image may be of the same scene or arrangement of objects, with the relative position of objects or portions of objects being different in one with respect to the other, to mimic the parallax between the images impinging on an observer""s left eye versus that impinging on his or her right eye. It is known in the art of imaging that a person""s perception of three dimensions, when viewing a real world scene, is caused, in significant part, by the parallax between the image seen by the person""s left eye and that seen by the person""s right eye. A typical camera does not capture this parallax, because it has only a single lens. Therefore, when a viewer looks at a photograph taken by a single-lens camera, his or her left eye and right eye see exactly the same image. There is no parallax conveyed. For this reason, a typical photograph does not convey a three-dimensional feel, and flattens the appearance of objects.
A lenticular sheet, though, permits display of an image on a hard copy surface to appear three-dimensional. One method for this displaying is to take a picture of a scene from a first location, and then move the camera a lateral distance to a second location and take a picture of the same scene. The picture taken from the first position may be called the left image and the picture taken from the second position may be called the right image. There is a parallax between the two images, due to the lateral displacement between the respective positions from which the left and right pictures were taken. The parallax is exploited by rasterizing the left and right images or pictures into, for example, sixty-four vertical strips each. The rasterizing can be done by converting the pictures into a digital pixel array and then dividing the array into sixty-four strips, typically in a vertical direction. The left and right images are disposed on a medium, typically by placing the first vertical stripe of the left image next to the first vertical stripe of the right image, and then the second vertical stripe of the left image next to the second vertical stripe of the right image. The arrangement is typically repeated so that, for example, the sixty-four vertical stripes of the left image are interspersed with sixty-four vertical stripes of the right image, in an alternating pattern.
A lenticular sheet having, for example, sixty-four lenticules is placed over the two interspersed rasterized images, such that each lenticule runs parallel to, and extends above, at least one left image raster line and one right image raster line. Because the left and right raster lines have different positions under the lenticules, the light from the left image raster line will have a different angle of refraction passing through the lenticule than does the light from the right image raster line. The different angles of refraction are such that a person""s left eye, when at a specific viewing angle and distance with respect to the medium, will see only the left image raster lines and the person""s right eye will see only the right image raster lines. The person""s left eye and right eye receive different images, the difference between the two being the parallax that the person would have actually observed if looking at the original scene. The person thus xe2x80x9cseesxe2x80x9d a three dimensional image.
Typically, placing two raster lines under each lenticule limits the viewing positions from which an observer will see a three dimensional image. The reason is that to see three dimensions the viewer must be in the position where only the left image raster lines are refracted to the viewer""s left eye, and only the right image raster line are refracted to the viewer""s right eye. At other viewing positions the viewer""s eyes each receive both the left image and right image raster lines, or both eyes receive only left image raster lines or right image raster lines, which presents as a two-dimensional image.
To increase the number of viewing positions from which the observer will see a three-dimensional image, a greater number of rasterized images are created, and a correspondingly greater number of raster lines are disposed under each lenticule. For example, instead of a left eye and right eye picture taken from a single head-on view, a plurality of left/right pictures can be taken, each from a different view. Picking three views as an example, the above-described head-on view is generated as described, and then a first flank view is generated by taking a left eye picture and a right eye picture, from a position to the left and right, respectively, of a second view position. The second view position may be displaced, for example, 10 degrees left from the head-on position. Next a right flank view is generated by taking a left picture and a right picture, from a position to the left and right, respectively, of a third view position. The third view position is displaced, for this example, 10 degrees to the right of the head-on position.
There are problems with the above-described multiple view method, though, arising from the requirement for more raster lines. For example, the three above-described views require six pictures or images, to be displayed through the lenticular sheet. For such display, each of the six images or pictures must be segmented or rasterized into, for example, sixty-four vertical strips. The sixty-four vertical strips of each picture or image would then be interleaved so that a total of 364 vertical strips, or raster lines, are disposed on the substrate. The lenticular sheet would then be overlaid such that each lenticule covers six vertical strips or raster lines, namely one from each of the left and right pictures taken from each of the three above-described viewing perspectives.
Due to the differing positions of each of the six raster lines under the lenticule, the light from each undergoes a different angle of refraction as it passes through the lenticule. Because of the raster lines from the different images being diffracted differently, there is typically one viewing position at which the observer sees a three-dimensional image of the above-described head-on view. Assuming the raster lines are disposed accurately with respect to the lenticules, there is a second viewing position at which the observer sees a three-dimensional image of the left flank view. Likewise, assuming the raster lines are disposed accurately with respect to the lenticules, there is a third viewing position at which the viewer will see a three-dimensional view from the right flank viewing angle.
There are problems with the multiple viewing angle method, namely that the method requires a greater number of pixel or raster lines. A related problem is that the method requires that the pixel or raster lines be disposed accurately with respect to the lenticules.
Lenticular sheets also allow observers to see images which change as the observer changes his or her position with respect to the medium. The principle of operation is the same as that used for presenting images appearing to be three-dimensional. An example is a first picture or image being of a golfer holding a club in the upswing position, and a second image being of the golfer in the downswing position. The two images or pictures are rasterized. The raster lines of the two images are disposed on a medium, typically in a manner alternating between a raster line from the first picture, i.e. The golfer in the upswing position, followed by a raster line from the second picture, i.e. The golfer in the downswing position. The pattern is continued such that the two rasterized images are interlaced with one another. Then, a lenticular sheet is typically overlaid such that each lenticule covers two raster linesxe2x80x94one raster line from the first picture and one raster line from the second picture.
Due to the different positions under the lenticule, the light from the raster line corresponding to the first picture or image is diffracted at an angle different than the light from the raster line of the second picture or image. The different diffraction angles are such that the observer from a first viewing position sees only the raster lines from one of the two pictures or images. However, when the observer is at a second position he or she sees only the raster lines from the other of the two pictures or images. Referring to the golf example, the observer would see the golfer in the upswing position from one viewing position but would see the downswing position from another viewing position.
The golfer example above used only two images. More than two images however, could be imaged, rasterized, disposed on a medium, and overlaid with a lenticular sheet. For example, a sequence of the golfer going through four positions can be displayed through a lenticular sheet as follows: First, the four positions would be photographed and rasterized. The four rasterized images would then be disposed on a printable medium or substrate. The arrangement would typically be the first raster line from each of the four pictures followed by the second raster line from each of the four pictures, and so on. A lenticular sheet would then be overlaid, typically such that each lenticule covered, for this example, four raster lines, one raster line from each of the four pictures. The location of each set of four raster lines under each lenticule is such that the observer sees only the raster lines from one of the four, depending on the viewing angle relative to the medium.
The above example of four positions of a golfer presents problems similar to the multiple three-dimensional images. Namely, the greater the number of images, whether the images are different views of the same scene or different positions or degrees of zoom for an object, the greater the number of pixel lines that are required. The general relation between image quality and the number of pixel or raster lines amplifies these problems. Stated differently, both the quality of an image and the number of images or views that can be seen though a lenticular sheet are determined, in significant part, by the number and spacing of the raster lines and by the number of lenticules or microlenses. However, for any given size of image an increase in the number of raster lines necessarily decreases the line width, or the width of each pixel making up the line if the image is pixel-based. The increase in the number of raster lines not only decreases the line or pixel width; it also decreases the spacing from one raster line or pixel to the next.
The present inventors have identified inkjet printers as a preferred apparatus for printing lines of pixels, or raster lines, for viewing through a lenticular sheet. However, inkjet printers have inherent limitations as to the minimum dot size they can print, and limitations on the minimum spacing from one dot to the next. The prior art selects line widths and spacing based on trial-and-error, or to match standard or vendor-supplied lenticular sheets. Prior art lenticular sheets, however, are manufactured without particular consideration to the specific printing capabilities of the printer, or of the type of printer, that will be used to print the interleaved pixel lines, i.e., raster lines, on the medium. The spacing between the lenticules or microlenses, though, is one of the ultimate factors bearing on the width of the pixel lines, and the number and spacing of pixel lines. More particularly, if the number of pixel lines is selected which results in a line, or pixel width, or pixel-to-pixel spacing smaller than the ink-jet printer can produce the image quality will be substantially degraded. On the other hand, if the number of pixel lines is selected based on an overly conservative estimate of the printer""s capabilities, the final product will have an image quality that is lower than what could have been obtained.
The present inventors have identified a further problem with using inkjet printers to print on a lenticular sheet. The problem is that, due to human error, shortcomings in the printer feed mechanism, and other causes, the orientation of the lenticular sheet when the printing operation is performed may not be correct. As a result, as the lenticular sheet progresses through the printer there will be a migration in the position of the first lenticule in the direction of the printer carriage.
Still another problem identified by the present inventors is that regardless of the nominal spacing between lenticules, the raster image processing associated with an inkjet printer cannot space the pixels as correctly as attainable absent use of measured data representing the lenticule spacing of the lenticule sheet that is actually being printed on.
These problems, and others, are overcome, and additional benefits are provided by the methods and apparati according to the present invention.
A first aspect of the invention includes steps of providing a microlens or lenticular sheet having a plurality of microlenses or lenticules extending in a first direction with a spacing between lenticules and having an ink-receptive surface disposed on a surface of the lenticular sheet, and providing a digital image data processing apparatus having a data storage, a data input/output interface, and raster image processing (xe2x80x9cRIPxe2x80x9d) software, and providing an inklet printer having a print head moved in a carriage direction by a servo, a light sensor for receiving an ambient light passing through the lenticular sheet and for generating a sensor signal in response, and a transmitter for transmitting the sensor signal to the input/output interface of the digital image processing apparatus, and a servo for moving the sensor in the carriage direction. Next, a digital image file representing, in pixel form, an image for printing on the lenticular sheet is stored in the image data storage of the digital image processing apparatus. The lenticular sheet is then fed or placed into the inkjet printer such that the lenticules extend in a direction perpendicular to the carriage direction. Next a scan step moves the light sensor in the carriage direction to detect light through the lenticular sheet at a sequence of positions along the carriage direction and transmits corresponding sensor data to the digital image processing apparatus. The digital image processing apparatus then calculates a lenticule spacing data, representing an estimated value of the lenticule spacing, based on the sensor data transmitted by the scan step. Next an image modification step generates a re-spaced digital image file based on the digital image file and the lenticule spacing data. A printing step then prints an image on the lenticular sheet corresponding to the re-spaced digital image file.
Another aspect of this invention includes provides the lenticular sheet by first providing an inkjet printer with a digital signal interface for communicating with a programmable computer or other digital image data processing and having a storage apparatus, and having a movable print head controlled by a servo. Next a measuring step measures the smallest increment that the servo can move the movable print head and generates a Least Interval Value data representing the measurement. Next, the sheet is extruded with lenticules having a spacing based on the Least Interval Value data, and preferably having an ink-receptive surface.